Render is incredibly Grainy!
Probable causes of noisy renders:
(click on the links in blue)


Render Samples set too low 100 samples might just be too low for what you want, try a higher value.

Here's the scene at 800 samples:


Samples set on render layer override regular sample settings.
Lights or environment not set to multiple importance. Aditionally this link
render resolution is set to less than 100%
Use branched path tracing instead of the default samples



Bring up the AA samples and then set the values for each type of sample according to the materials in your scene. Note that each of this values is multiplied by that of the AA Samples. (for example 4 diffuse will turn into 500 samples when the AA value is set to 125)